Voice communication systems, including telephone systems, are subject to several sources of echo that make transmitted voices sound bad to listeners. These echoes can noticeably degrade the intelligibility and quality of the transmitted voice signal. One source of echo is simple acoustic reverberation at the talker's physical location. Echoes associated with acoustic reverberation at the talker's physical location are particularly evident in connection with speaker phones. However, it is often the case that people speaking into a speakerphone within small enclosed environments, such as offices or conference rooms, are unaware of such echoes.
Attempts at reducing echo in transmitted voices have included physically modifying room acoustics. Such physical modifications can be made by, for example, placing echo dampening material on the walls and ceilings. However, such modifications can be expensive. In addition, such modifications may not be possible or appropriate to all rooms in which the use of a speaker phone is desirable. Furthermore, a change in the arrangement of furniture in a room, or in the position of the speaker phone within the room, can result in the introduction of echo to a transmitted voice signal, even though previously there had been no echo.
Other attempts at reducing echo in outgoing signals have included placing individual microphones as close as possible to talkers. For example, requiring talkers to speak into microphones positioned directly in front of the talker's mouth, for example as part of a handset or headset, can be effective in reducing acoustic echo. However, it is not always convenient or desirable to hold a handset or to wear a headset. Furthermore, although microphones can be placed in front of individual talkers, for example in a conference call scenario with multiple talkers at a location using a speaker phone, the problem of acoustic reverberation at the physical location may not be entirely avoided.
Still another attempt at reducing the effect of echo or acoustic reverberation in outgoing voice communication signals is the use of highly directional microphone designs. Directional microphones may be deployed singly or in arrays, and are capable of accepting or rejecting sounds depending on their point of origin. However, directional microphones are relatively expensive, can be difficult to properly set up, and do not work well when a talker is moving about their physical location.
Yet another attempt at reducing echo in voice communications is the use of signal processing techniques to compensate for or remove the echo. Generally, such techniques require the deployment of a digital signal processor capable of detecting and compensating for the echo. Although such techniques can be effective at reducing the effects of acoustic reverberation, they are relatively expensive to develop and deploy.